1. Field of the Invention
The present invention relates to a driving device, and more particularly to a driving device for a milling machine.
2. Description of the Prior Art
A typical driving device for a milling machine is disclosed in FIG. 7 and comprises a cylinder 50 including a number of posts 51 extended upward therefrom, a chamber 52 formed in the bottom portion, a mouth 53 for supplying pressurized air into the cylinder 50, a piston rod 54 slidably extended into the cylinder 50 and a piston 55 slidably engaged in the cylinder 50, a pneumatic driving mechanism 56 disposed on top of the piston 54 and moving in concert with the piston 55, an engaging surface 57 formed in the piston 55, and a rod 61 including a head 62 formed in the upper end for engagement with the engaging surface 57 when the piston 55 moves downward, and a milling cutter 64 threadedly engaged to the lower end of the rod 61. The pneumatic driving mechanism 56 is provided to rotate the rod 61 so as to threadedly engage the rod 61 to the cutter 64.
However, the whole pneumatic driving mechanism 56 is supported on the piston rod 54 and moves in concert with the piston rod 54, such that a great pneumatic power is required to move both the piston rod 54 and the pneumatic driving mechanism 56. In addition, the center of gravity of the pneumatic driving mechanism 56 is highly elevated such that the mechanism 56 can not be stably supported in place, and such that shocks and vibrations and thus noise may occur. Furthermore, the stroke of the piston 55 is predetermined and can not be changed such that the mechanism 56 is suitable for driving only one type of the rods 61.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional driving devices for milling machine.